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178 lines
4.4 KiB
ArmAsm
178 lines
4.4 KiB
ArmAsm
/* strchr with SSE4.2
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Copyright (C) 2009 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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#include <sysdep.h>
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#include <ifunc-defines.h>
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/* Define multiple versions only for the definition in libc. */
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#ifndef NOT_IN_libc
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.text
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ENTRY(strchr)
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.type strchr, @gnu_indirect_function
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cmpl $0, __cpu_features+KIND_OFFSET(%rip)
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jne 1f
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call __init_cpu_features
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1: leaq __strchr_sse2(%rip), %rax
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testl $(1<<20), __cpu_features+CPUID_OFFSET+COMMON_CPUID_INDEX_1*CPUID_SIZE+CPUID_ECX_OFFSET(%rip)
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jz 2f
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leaq __strchr_sse42(%rip), %rax
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2: ret
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END(strchr)
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/*
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This implementation uses SSE4 instructions to compare up to 16 bytes
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at a time looking for the first occurrence of the character c in the
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string s:
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char *strchr (const char *s, int c);
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We use 0xa:
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_SIDD_SBYTE_OPS
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| _SIDD_CMP_EQUAL_EACH
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| _SIDD_LEAST_SIGNIFICANT
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on pcmpistri to compare xmm/mem128
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0 1 2 3 4 5 6 7 8 9 A B C D E F
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X X X X X X X X X X X X X X X X
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against xmm
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0 1 2 3 4 5 6 7 8 9 A B C D E F
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C C C C C C C C C C C C C C C C
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to find out if the first 16byte data element has a byte C and the
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offset of the first byte. There are 3 cases:
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1. The first 16byte data element has the byte C at the offset X.
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2. The first 16byte data element has EOS and doesn't have the byte C.
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3. The first 16byte data element is valid and doesn't have the byte C.
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Here is the table of ECX, CFlag, ZFlag and SFlag for 3 cases:
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case ECX CFlag ZFlag SFlag
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1 X 1 0/1 0
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2 16 0 1 0
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3 16 0 0 0
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We exit from the loop for cases 1 and 2 with jbe which branches
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when either CFlag or ZFlag is 1. If CFlag == 1, ECX has the offset
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X for case 1. */
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.section .text.sse4.2,"ax",@progbits
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.align 16
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.type __strchr_sse42, @function
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__strchr_sse42:
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cfi_startproc
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CALL_MCOUNT
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testb %sil, %sil
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je __strend_sse4
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pxor %xmm2, %xmm2
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movd %esi, %xmm1
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movl %edi, %ecx
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andl $15, %ecx
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movq %rdi, %r8
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je L(aligned_start)
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/* Handle unaligned string. */
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andq $-16, %r8
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pshufb %xmm2, %xmm1
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movdqa (%r8), %xmm0
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pcmpeqb %xmm0, %xmm2
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pcmpeqb %xmm1, %xmm0
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/* Find where NULL is. */
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pmovmskb %xmm2, %edx
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/* Check if there is a match. */
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pmovmskb %xmm0, %esi
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/* Remove the leading bytes. */
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sarl %cl, %edx
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sarl %cl, %esi
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testl %esi, %esi
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je L(unaligned_no_match)
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/* Check which byte is a match. */
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bsfl %esi, %eax
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/* Is there a NULL? */
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testl %edx, %edx
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je L(unaligned_match)
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bsfl %edx, %esi
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cmpl %esi, %eax
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/* Return NULL if NULL comes first. */
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ja L(return_null)
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L(unaligned_match):
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addq %rdi, %rax
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ret
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.p2align 4
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L(unaligned_no_match):
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testl %edx, %edx
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jne L(return_null)
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/* Loop start on aligned string. */
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L(loop):
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addq $16, %r8
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L(aligned_start):
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pcmpistri $0x2, (%r8), %xmm1
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jbe L(wrap)
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addq $16, %r8
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pcmpistri $0x2, (%r8), %xmm1
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jbe L(wrap)
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addq $16, %r8
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pcmpistri $0x2, (%r8), %xmm1
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jbe L(wrap)
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addq $16, %r8
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pcmpistri $0x2, (%r8), %xmm1
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jbe L(wrap)
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jmp L(loop)
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L(wrap):
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jc L(loop_exit)
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/* Return NULL. */
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L(return_null):
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xorl %eax, %eax
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ret
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/* Loop exit. */
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.p2align 4
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L(loop_exit):
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leaq (%r8,%rcx), %rax
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ret
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cfi_endproc
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.size __strchr_sse42, .-__strchr_sse42
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# undef ENTRY
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# define ENTRY(name) \
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.type __strchr_sse2, @function; \
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.align 16; \
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__strchr_sse2: cfi_startproc; \
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CALL_MCOUNT
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# undef END
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# define END(name) \
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cfi_endproc; .size __strchr_sse2, .-__strchr_sse2
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# undef libc_hidden_builtin_def
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/* It doesn't make sense to send libc-internal strchr calls through a PLT.
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The speedup we get from using SSE4.2 instruction is likely eaten away
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by the indirect call in the PLT. */
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# define libc_hidden_builtin_def(name) \
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.globl __GI_strchr; __GI_strchr = __strchr_sse2
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#endif
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#include "../strchr.S"
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